MRI utilization in ischemic stroke has increased substantially from 1999 to 2008. Growth in MRI utilization was seen in every year in every state in our study population. In high utilizing regions, the rate has plateaued at a level suggesting that nearly all eligible patients are receiving MRI.32, 33
Yet, 95% of patients receiving MRI also received CT; MRI is not replacing CT as the primary stroke neuroimaging study, instead receipt of multiple neuroimaging studies is increasingly common. In addition to an increase in overall MRI utilization, we also observed marked geographic variation. In 2008, 55% of stroke patients underwent MRI in Oregon compared to 79% in Arizona. Partly as a consequence of this widespread increased use, diagnostic imaging has been the fastest growing cost component of stroke care. These data suggest that neuroimaging practices in stroke are neither standardized nor efficient.
The wide geographic variation in MRI utilization demonstrates a potential opportunity to improve stroke care by increasing standardization. This variation was not accounted for by measurable patient characteristics or hospital acquisition of MRI technology. While we cannot directly measure patient preferences, there is little evidence that patients have strong and variable preferences among imaging modalities, independent of the advice of their physicians;34
it is further unclear why those preferences would be so geographically variable so as to explain the observed pattern. Absent a credible alternative explanation, variation in physician practice patterns likely accounts for much of the variation in MRI utilization
The existence of variation in physician practice in this context is not surprising as variation tends be greater when the evidence for a practice is less certain29
and stroke imaging guidelines during the study period did not preferentially recommend CT or MRI.15, 17
Recent guidelines have generally made more favorable recommendations regarding MRI than previous guidelines, but inconsistency between these guidelines exists. Recently, an American Heart Association (AHA) Scientific Statement was the first major guideline to recommend routine use of MRI or CT angiography for stroke patients.35
The recent American Academy of Neurology (AAN) guideline on the role of MRI in stroke36
limits its preferential recommendation of MRI to the period within 12 hours of stroke onset. The most recent European Stroke Organization (ESO) guideline37
calls for stroke patients to receive either CT or MRI. Standardization of neuroimaging practices may improve as guidelines become more consistent, particularly if evidence emerges that MRI leads to improved outcomes or more optimal physician decision-making. The current highly variable use of MRI suggests that there may be community equipoise that would make a randomized trial ethical, feasible and useful.
Not only are stroke neuroimaging practices non-standardized, but our findings suggest stroke neuroimaging may be unnecessarily costly. In our sample, 95% of patients receiving a MRI also received a CT, thus minimizing the use of multiple imaging studies may represent a viable strategy to contain neuroimaging costs. If the practice of obtaining both MRI and CT reflects physician preference for MRI in a context where CT can be obtained more quickly, then several broad strategies for increasing efficiency are possible. First, some patients may be able to safely wait for an imaging study, allowing MRI to be performed without a preceding CT. Patients with delayed presentations, out of the acute treatment window, and stable examinations might meet these criteria and represent a significant proportion of all stroke patients. Up to 36% of stroke patients present more than 12 hours after onset.38
Second, wider dissemination of rapid stroke MRI protocols relying on a selective set of sequences (ie: diffusion-weighted, gradient-echo and T2-weighted sequences) may minimize resource utilization and allow for quicker scanner turnover thus enabling earlier MRI acquisition.39
For MRI to be a viable alternative to CT in the acute stroke period, scan times for MRI must not be greater than CT to minimize time delay for thrombolysis.
This study has several important limitations. First, the use of administrative data to identify stroke is an imprecise process raising the possibility that some of the variability in MRI utilization and cost may be due to imprecision in coding of stroke diagnoses. To minimize this, we have used a previously validated algorithm to identify stroke cases.19
Similarly, revenue code-based identification of imaging studies is also limited by the inability to reliably identify the subcomponents of an imaging study, the number of times an individual patient received a given neuroimaging study which body part was imaged, or the timing of imaging studies. Consequently, we are unable to reliably determine the role of MRA compared to MRI, which portion of studies were focused on the CNS or when imaging studies were obtained during the hospitalization. Because of this limited information, we can not speculate as to why physicians obtained an MRI in an individual case (ie: was MRI obtained to aid thrombolysis decision making, clarify diagnosis or inform secondary prevention strategies?) Additionally, while our dataset was selected to maximize geographic and demographic variability, the southern states and African Americans are underrepresented.
The use of MRI in ischemic stroke has substantially increased over the last decade, with wide geographic variation and increasing contribution to the cost of stroke care. These findings emphasize the importance of future research to define which stroke patients are likely to benefit from MRI, how MRI information should be applied to individuals, and the relationship between MRI and clinical meaningful outcomes. Finally, these findings illustrate the potential to reduce variability and improve the efficiency of neuroimaging in stroke.